(NewsTarget) Scientists at the University of Washington and Veterans Association Puget Health Care System in Seattle studied the link between testosterone levels and death in 858 military veterans over 40, and found that those with lower levels were more likely to die earlier.

The health records of the military veterans, who had their testosterone levels checked at least twice between 1994 and 2002, showed that 53 percent had normal levels, 28 percent had fluctuating levels with a normal average level, and 19 percent were classified as having low levels.

After removing the results of any veteran who had died within a year of their second testosterone sample, then compensating for factors such as age, body mass index and illness, the researchers found that the mortality risk for men with low testosterone was 68 percent higher than those with normal levels of the hormone.

"The persistence of elevated mortality risk after excluding early deaths suggests that the association between low testosterone and mortality is not simply due to acute illness," wrote study co-author Molly Shores, adding that because the study focused on veterans, who are already at an increased mortality risk, the results might not be applicable to the general public. "Large prospective studies are needed to clarify the association between low testosterone levels and mortality," she said.

Pierre Bouloux, professor of endocrinology from the Royal Free Hospital in London, said the fact that the study was retrospective rather than prospective was "not helpful."

"As the authors themselves state, to pursue any association, you really need a prospective study," he said.

Bouloux also noted that the study's focus on veterans skewed its results, because the health records were taken from a Veterans Association hospital and most people who are treated there are of low socioeconomic status. Poverty and socioeconomic status are known to have an impact on mortality, according to Bouloux.

"It also seems very odd to me that the mortality amongst all of the men is so high but the problem is that the study does not even tell us what the causes of the deaths are," he said.